A Real Shocking Discovery

Scientists have discovered a new species of eel that can discharge up to 860 volts of electricity – significantly more than the 650 volts previously recorded by what had been believed to be the only type of eel in existence… until now.

The electric eel is actually not an eel at all, but a member of the knifefish Order Gymnotiformes which is most closely related to catfishes. For the past 250 years, scientists believed the genus contained only one species that is widely distributed in northern South America east of the Andes.

Scientists looked at patterns of genetic, morphological and ecological data in the “single species” of electric eel distributed throughout Greater Amazonia. Their analyses support the identification of three major lineages, two of which warrant recognition as new species.

mark in water
Mark Sabaj waits for an eel to break surface.

Mark Sabaj, PhD, interim curator of fishes at the Academy of Natural Sciences of Drexel University is well-versed in techniques for catching electric eels both with and without getting shocked. He contributed to a large study of electric eels as a member of a multinational team led by Carlos David de Santana, an ichthyologist at the National Museum of Natural History in Washington, D.C. Sabaj is a co-author on the descriptions of two new species, Electrophorus voltai and Electrophorus varii, published Tuesday in Nature Communications.

Sabaj recounts his role in the capture of the new eels and the marvels of this discovery.

Scientists believed for centuries that there was only one species of electric eel, why investigate this hypothesis now?

The taxonomic study of a widely distributed species presents a variety of challenges. For starters, you need to have enough specimens from throughout its range to confidently assess patterns of morphological, genetic and ecological variation. Electric eels occur in at least nine different countries – so, that is a lot of ground to cover. Some parts of its range are well-sampled and provide a good number of specimens for study in museums, like the Academy of Natural Sciences of Drexel University. More remote areas, like the Xingu River, had to be newly sampled. So the time was right to ask a big question – is there more than one species of electric eel? The answer is yes.

When did you begin to realize you had discovered not one, but two new species of electric eel?

Well, David Santana has been studying the diversification of knifefishes for over 20 years and he has probably examined more museum specimens than any other ichthyologist living or dead. Early on, he visited the Academy of Natural Sciences and shared his thoughts on Electrophorus, some of which were based on a master’s study by his student Natália de Castro e Castro. David knew I was working in the Xingu and asked me to be on the lookout for electric eels because he thought there was a new species on the Brazilian Shield.

So, it was more a matter of finding the Xingu eels to test his hypothesis. David also had a hunch that the lowland electric eels were distinct from the upland ones on the Guiana and Brazilian Shields. The two shields were more connected in the distant past and probably supported a single species of electric eel. The Amazon River began to bisect the shields about 9 million years ago. This created an ecological barrier between the two shield populations that allowed them to differentiate into separate species. Similar patterns of speciation are known for other fishes, so this study was less about “discovery” and more about testing a reasonable hypothesis based on our knowledge of other Neotropical fishes.

What prep goes into collecting the specimens?

A tremendous amount of prep work goes into collecting specimens, from getting vaccinations and visas to teaming up with local fishermen who know the best places to look for your target species. Finding the right place at the right time does not guarantee that you will catch your fish (ask any angler). So, capturing the fish you seek is a tremendous reward.

In the Xingu, we used a large hook on the end of a wooden pole to gaff eels when they break the water’s surface to breath air. Unlike most fishes, electric eels have only vestigial gills. As obligate air breathers, electric eels regularly gulp atmospheric air and use an oral respiratory organ to extract oxygen (see photo). While fishing, the trick is to balance above the water, on a fallen tree for instance, while lunging your gaff at the eel. If you slip into the water with an eel on your hook…you get shocked!

Have you ever been shocked? What’s it like?

Yes, I have been shocked a few times. When you are fishing for electric eels, anticipation fills your body with adrenaline. The shocks just add to the rush. When you are not expecting it, an encounter with an electric eel can be surreal. As in, why am I being shocked when I am hip high in muddy water and miles away from the nearest electrical grid.

How likely are people to come in contact with one of these eels?

Most people will spend their entire lives without seeing an electric eel outside of a public aquarium or nature program. Even those who visit the Amazon Basin to swim in its waters are unlikely to encounter an electric eel. Electric eels are nocturnal, highly secretive and occupy specific habitats – so, you really need to look for them. That said, it is best to avoid woody debris and aquatic vegetation along river margins and in shallow secluded pools when entering the tropical waters of northern South America.

Why is this discovery important?

People often point out that new species may somehow yield new cures to human ills. In rare cases that is certainly true. But, in most cases it is not. The importance of new species discoveries lies in a better understanding of biodiversity and evolution. In this case, we have a better understanding of diversity in electric eels, how this diversity is distributed in South America, and what historical events might have promoted the evolution of this diversity.

electric eel in mud
Xingu electric eels regularly have a pattern of light botches on their anterior sides, but lack the reddish coloration on the undersides of the head and abdomen seen in other populations. Photo by Mark Sabaj/ANS

A variety of recent projects, including two at the Academy funded by the U.S. National Science Foundation (All Catfish Species Inventory, iXingu Project), allowed the researchers to assemble enough specimens for a comprehensive study. Lead author David Santana also received funding from the Brazilian state of São Paulo to conduct a comprehensive revision of the entire knifefish Order Gymnotiformes.


By Emily Storz

One comment

  1. Very interesting. I only saw one electric eel in my life and that was down in Atlantic City, NJ at Steel Pier when it was on display for years there, when I was a child. I enjoy reading and looking at all of Mark’s adventures. I’ve been to his presentations and again, enjoy them and quite educational. Keep up the good work Mark.

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